In a Long Term Evolution (LTE) system, downlink communication services may be divided into two categories, i.e., a unicast service and a Multimedia Broadcast Multicast Service (MBMS), where the former refers to a point-to-point service of transmitting data from a data source to a User Equipment (UE) and the latter refers to a point-to-multipoint service of transmitting data from a data source to a plurality of user equipment.
In a radio access network, multicast and broadcast of both an all-text message at a low rate and a multimedia service at a high rate may be implemented in an MBMS by using a common transport channel and a common radio bearer.
However, an existing MBMS broadcast in a mobile cellular network has no possibility of notifying system time to a UE. An MBMS control channel generally is an MBMS multipoint Control CHannel (MCCH), and an MCCH message includes the following information:
1. MBMS access information;
2. MBMS common point-to-multipoint (p-t-m) radio bearer information;
3. MBMS current cell point-to-multipoint (p-t-m) radio bearer information;
4. MBMS general information;
5. MBMS modified services information;
6. MBMS neighboring cell point-to-multipoint (p-t-m) radio bearer information; and
7. MBMS unmodified services information.
Particularly, the MBMS access information is responsible for passing a parameter of an MBMS counting process, and since no counting process is configured in an operation of an MBMS Single Frequency Network (MBSFN), a UE may not fetch this parameter; the MBMS common point-to-multipoint (p-t-m) radio bearer information is responsible for configuration of the respective Radio Bearers (RBs); the MBMS current cell point-to-multipoint (p-t-m) radio bearer information is responsible for configuration of an RB of a current cell; the MBMS general information is responsible for configuration information of an MBMS Indicator CHannel (MICH) and information of some counters; the MBMS modified services information is responsible for passing information on a modified service; the MBMS neighboring cell point-to-multipoint (p-t-m) radio bearer information is responsible for passing information on an RB of a neighboring cell; and the MBMS unmodified services information is responsible for passing information on an unmodified service.
At present, a UE acquires an MBMS service in the following procedure: when a separate Secondary Common Control Physical CHannel (SCCPCH) carries merely an MBMS service, the UE fetches a System Information Block (SIB) 5 first and retrieves MBMS configuration information from the Secondary Common Control Physical CHannel (SCCPCH) system information of the MBMS, and after knowing configuration information of an MCCH of the MBMS, the UE can locate the MCCH among corresponding physical and transport channels and fetch MBMS modified services information and MBMS unmodified services information and also MBMS general information to retrieve configuration information of an MICH and possibly some information on a preferred frequency, a timer (T318), a counter and a cell group identity and also optional configuration information of an MBMS point-to-multipoint Scheduling CHannel (MSCH). If there is the MBMS service to be received by the UE, then the UE receives the corresponding MBMS service directly. If there is no MBMS service to be received by the UE, then the UE listens to the MICH.
As can be apparent, the UE fetches the SIB5first, then finds the MCCH from the SIB5 and the configuration information of the MICH from the MBMS general information in the MCCH and next listens to the MICH to determine the arrival time of the MBMS service to be received by the UE.
The UE receives the MCCH information starting from the next modification cycle notified in notification information upon determining the arrival of the MBMS service to be received by the UE. The UE knows from the MCCH whether the specific service arrives and a specific location of the arriving service and configures a corresponding bearer to receive the MBMS service starting from the next modification cycle.
However in view of the unidirectional downlink of an MBMS broadcast network, the UE cannot request a network server for system time information. No system time information of the network side is carried on the MCCH, and the time of the UE (including the time of respective applications in the UE) has to depend only upon its own setting and the UE cannot revise the local time to the time of the network side, so that the time of the UE may be inconsistent with that of the network side and consequently the UE cannot receive the MBMS service normally.
For example, a data unit (slice) of a TV program is validated at (valid from) 19:00 and invalidated at (valid to) 19:30, and a user equipment accesses a channel under the control of parameters including a start time, an end time, etc., of a distribution window of the data unit (slice) in a schedule and presents contents of a service under the control of parameters including a start time, an end time, etc., of a presentation window, but this mechanism is effected on the precondition that the time of the user equipment can be kept consistent with the system time of the network side; otherwise, the service would not be offered as expected. For example, the data unit (slice) of the program is validated at (valid from) 19:00 and invalidated at (valid to) 19:30, but there is a one-hour difference between the time locally set at the user equipment and the system time of the network side, so that the slice of the program is validated and invalidated at some unexpected time.
In view of the foregoing, the system time of the network side can not be notified to the UE in the MBMS mechanism in the prior art, thus making it impossible to ensure normal reception of an MBMS service at the UE.